Police in Barcelona have arrested 39 members of a suspected Chinese mafia and freed 30 young Chinese women whom they allegedly forced into prostitution, a senior officer of the Catalan regional police told CNN Wednesday.

The arrests occurred earlier this week after a long investigation. It was the biggest strike to date against Chinese-run mafias involved in forced prostitution in the northeast region of Catalonia, whose capital is Barcelona, said the senior officer, Xavier Cortes, head of the Catalan police unit that fights human trafficking.

In recent years, the Chinese crime syndicate had crowded out others from the prostitution market in the fashionable Eixample district of Barcelona by using forced prostitution and charging below-market rates, Cortes said.

The women were forced to work in unsanitary conditions and in marathon sessions, seeing eight clients in a row for an hour each, he said.

After initial arraignments, a judge ordered 33 of the suspects to remain in prison. Six others were released but remain under investigation, and must check in regularly with authorities, Cortes said.

Police are searching for six additional suspects, Cortes said. A total of 17 brothels were dismantled.

The 30 women were initially placed in special assistance centers run by a non-governmental organization, but some have now left to live with friends in Barcelona, he said.

The suspected Chinese mafia also was involved in document forgery, said Joaquim Frances, of the Catalan police organized crime unit, at a news conference Wednesday in Barcelona.

"In addition to prostitution, the gang also was involved human trafficking," Frances said. "Barcelona was the hub used to later send these people to the United States, Australia and Canada. So for a time, they were kept against their will in Barcelona or nearby until they were provided with documents in order to travel to these countries."

In numerous raids, the police seized forged passports from many countries -- what Cortes called "perfect and very dangerous false documents" -- as well as the machinery to make them.

The Chinese mafia also was involved in drug trafficking, and police seized some weapons in the raids, Cortes added.

The Catalan police broke up a forced-labor scheme involving Chinese clothing sweatshops in 2009, freeing several hundred victims and arresting more than 100 suspects.

But across the nation, police and non-governmental organizations say the biggest problem of modern-day slavery in Spain is forced prostitution, involving not just Chinese women, but also women from Latin America, North Africa and Eastern Europe.

Last year, Spanish police broke up a ring that tricked Brazilian men into coming to Spain and then forced them to work as male prostitutes.